Spraying of thermosetable materials such as by electrostatic deposition provides a powder coating process producing accurate and consistent layer thickness. Deposition by spraying is common with a variety of curable materials including inks, epoxies, polyesters, ceramics and other materials that are cured shortly after deposition. However, deposition of adhesive materials that are to be subsequently heated to coalesce without activation after deposition and then to be activated by heat has faced a number of challenges, specifically related to issues of creating a suitable free flowing powder form of the adhesive without particle agglomeration and without premature unwanted activation of the adhesive. Additionally it is desirable that the adhesive once deposited on a substrate is dry and non-tacky to the touch and furthermore it is preferable that the adhesive is solvent free to avoid the formation of volatile organic compounds. It is also important that the adhesive has a cure cycle whereby cure can be accomplished at a later activation stage perhaps at a different location. Additionally adhesive powders may have a tendency to form agglomerates and to create sticky substrates, both of which reduce the effectiveness and usability of the adhesive layer.
In United States Patent Application Publication 2014/0027039 we describe a method for forming an adhesively bonded article, comprising the steps of providing at least one first substrate having at least one first surface, and electrostatically delivering particles for forming a precursor layer to the at least one first surface. The particles may include precursors for defining a latent curing polymeric material that exhibits adhesive characteristics upon curing, wherein the particles of the precursor layer have an average size in the range of about 20 to about 150, preferably 50 to 100 microns. The particles may be of a solid precursor formulation that is substantially free of any solvent. The particles of the sprayed layer may then be physically transformed to form a substantially non-oriented fused precursor layer film that is tack-free and dry to the touch while on the at least one first surface and substantially entirely throughout the period to which it remains unexposed to a reaction activation condition. The precursor layer film may have a generally uniform thickness of less than about 0.3 mm. The precursor layer film may be subjected to a reaction activation condition to cause cross-linking and to define a cross-linked reaction product material that adhesively bonds the at least one first substrate with the at least one second substrate.
According to US 2014/0027039 one or both of the first substrate or the second substrate may be a metallic material. Alternatively one of both of the first substrate or the second substrate may be a polymeric or composite material.